This invention relates generally to flow control valves for refrigeration systems and particularly to a valve having a passage through the piston arranged to provide a superior balancing system to reduce loading on the motor means.
In the prior art valves are known which provide a piston and valve port between the inlet and outlet for controlling refrigerant flow through the valve. The piston is subjected to pressure from various sources to control movement of the piston between an open and a closed position. It is an advantage to provide a balancing force on the remote side of the piston tending to equalize the force on the inlet side of the piston resulting from inlet pressure. Essentially, the equalizing force is provided by means of an equalizing passage through the piston and by providing a pressure surface on each side of the piston, which is subjected to the inlet pressure.
Two known examples of such force balancing systems in thermostatic expansion valves are provided by U.S. Pat. Nos. 3,402,566 and 3,742,722, both valves having limited stroke from the mechanical action of the diaphragm. In U.S. Pat. No. 3,402,566 the pressure surface on the inlet side of the piston and the pressure surface on the remote side of the piston are connected by a communicating passage. The pressure surface areas are arranged so that when the valve is in the closed position, the area on the inlet side of the piston is less than the area on the remote side resulting in a net force tending to maintain the valve in the closed position. When the valve is in the open position, the pressure surface areas on each side of the valve are arranged to be the same providing a balanced force on the piston from inlet pressure.
In U.S. Pat. No. 3,742,722, a piston having a passage between two opposed pressure surfaces is disclosed and there is a similar arrangement to that for U.S. Pat. No. 3,402,566, except that the piston of U.S. Pat. No. 3,742,722 is provided with a nose piece which is selectively shaped to determine the valve flow capacity.
Another known expansion valve of interest is U.S. Pat. No. 4,911,404 which also includes an equalization passage through the piston and which is driven by a stepper motor actuator. These three commonly owned patents are incorporated herein by reference.
The present valve piston balancing system represents an improvement over these prior art valves and other similar valves in a manner not disclosed in the known prior art.
This flow control valve for a refrigeration system provides a balanced piston system by utilizing an equalization passage having a valve port in the piston communicating with the inlet and located to facilitate controlled pressure distribution in the valve operation thereby reducing load on the actuator.
The flow control valve comprises a body including an inlet, an outlet, and a passage communicating between the inlet and outlet and a valve chamber. The valve includes a valve port in the passage defined by a valve seat; a piston movably mounted in the valve chamber; and actuator means for moving the piston toward and away from the valve seat. The piston includes an equalization passage with an upper port and a lower port, the piston being capable of modulation in an open position in which the piston is spaced from the valve seat to define a zone of pressure lower than the inlet pressure. The upper port communicates with the valve chamber during modulation, and the lower port communicates with the zone of low pressure during modulation to provide a selected pressure variation in the valve chamber.
It is an aspect of this invention to provide that the equalization passage includes a lateral passage defining the lower port.
It is another aspect of this invention to provide that the piston includes a nose piece having a frusto-conical configuration.
It is yet another aspect of this invention to provide that the piston includes an outer portion and an inner portion interfitting the outer portion, the inner portion providing the frusto-conical nose piece.
It is still another aspect of this invention to provide that the equalization passage includes a lateral passage extending through the frusto-conical nose piece defining opposed ports.
It is an aspect of this invention to provide that the nose piece includes an end face and the lateral port is disposed a predetermined distance from the end face to selectively locate the lower ports relative to the valve seat.
It is an aspect of this invention to provide that the flow control valve may be used in a refrigeration system having a compressor, a condenser, an evaporator, the flow control valve providing an expansion valve operatively connected between the high pressure condenser side and the low pressure evaporator side.
It is another aspect of this invention to provide that the piston is movable from a closed position, in which the piston operatively engages the valve seat, and an open position in which the piston is spaced from the valve seat to define a zone of low pressure lower than the inlet pressure, the upper port communicating with the valve chamber when the piston is in a closed position and when the piston is in an open position, and the lower port communicating with the inlet chamber when the piston is in a closed position and the lower port communicating with the zone of low pressure when the piston is in an open modulating position to provide a selected pressure in the valve chamber to reduce imbalance forces.
It is an aspect of this invention to provide that the actuator means includes a stepper motor.
This flow control valve with lateral port balancing is inexpensive to manufacture, easy to install and operates efficiently for its intended purpose. The valve may be used in a refrigeration system as an expansion valve or a hot gas by-pass valve.